Known heat exchange systems can be used for different purposes, such as for heating water used for domestic, commercial or industrial purposes. For example, a hotel or the like establishment is required to make hot water available upon demand by its clients, such as for warm showers. At certain times during the day, almost no hot water demand occurs, while at certain other times during the day, very high hot water consumption occurs. Also, the main hotel heating system may be of the water-heating type, wherein hot water is circulated in thermally-conductive pipes that run throughout the hotel rooms.
Conventional heat exchange systems used to heat the water, for example used either by the hotel clients or for the hotel heating system, comprise two fluid circuits. Water to be heated circulates in the first fluid circuit in a liquid state. Water vapor circulates in the second fluid circuit at high temperatures (well over 212° F. or 100° C.). Both fluid circuits pass through a heat exchanger unit wherein the water to be heated will flow in pipes running through the heat exchanger unit, and wherein the hot water vapor will flow on the shell side of the heat exchanger through heat exchanger baffles around the pipes, transferring the heat through the thermally conductive pipes (and baffle plates) to the water to be heated. The water consequently exits the heat exchanger unit in a heated state. If the demand for hot water increases, the flow rate of the hot water vapor can be increased, and vice-versa.
Two main problems are related to these prior art systems. The first problem is that the efficiency of the heat exchange system is low, energy-wise. The second problem is that the temperature of the heated water at the outlet will vary according to outgoing water flow rate variations and/or according to incoming water temperature variations. This is especially true at low working-load of heat exchange systems (the low working-load of a heat exchange system is usually defined as 40% or less of its capacity, and the high working-load is usually defined as more than 40% of its capacity). Indeed, since the water flow rate through the heat exchanger unit may vary according to the demand, and/or since the temperature of the incoming water may also vary, the quantity of energy transmitted to the heated water cannot be precisely calibrated, and consequently the outlet temperature of the heated water cannot be regulated very precisely. The very high temperature of the hot water vapor (well over 212° F. or 100° C.), although necessary to rapidly heat the water in high working-load operation of the heat exchange system, also promotes this lack of precision in heating the water, since the very hot water vapor will often be too hot for a low working-load operation of the heat exchange system wherein a low quantity of energy is required. The disadvantageous consequence of this problem is that the outlet water transmitted will have a temperature which will vary relative to the desired water temperature. It is not uncommon to see water temperatures vary of 20° F. (11.1° C.) and more relative to the desired water temperature in conventional heat exchange systems.